In order to help your niece we do need more detail, OP. No identifying details.
In addition to @FatOaf ’s questions:
Did this happen at a university, an FE College, or another type of institution? (If the last, please specify as best you can)
Is the staff member a ‘regular’ member of staff such as a lecturer, reader or professor? Or are they a postdoctoral researcher, postgraduate student or other temporary/ auxiliary staff member? This is relevant for the politics of the situation. I don’t need the title, just which of the two broad categories the person belongs to.
Does the staff member if ‘regular’ hold a position formally giving them a say over your niece’s progression? In addition to the answer to @FatOaf ’s first question, I am referring to School or Departmental service/admin positions such as Senior Tutor, Examinations Officer, Director of Undergraduate Studies, etc - every place will have its own titles. I don’t need the title, just to know if they have such involvement.
True impropriety at university can be fought. In a traditional degree programme, the only way a student fails to progress is by failing their exams ( which are externally moderated).
FYI: At most unis students can make appointments to view their exams (under supervision). Also, at my uni and others I know exams are marked anonymously and by teams, and the marking is reviewed internally before external moderation. Your niece should have this option, perhaps at the start of next term
If your niece is doing a traditional degree programme, at first glance I am having difficulty seeing how there could be a link between the two things. But if you answer these questions, we and I am sure others will be happy to think more carefully about the situation with you.
We don’t need details about the bullying or the name of the institution or degree programme, and we’ve been careful not to ask for information that could be outing.